This application relates generally to spark plugs for internal combustion engines and, more particularly, to the construction of ground electrodes for such spark plugs. More particularly, the present invention relates to attachment of a noble metal tip to such a ground electrode.
Conventional spark plugs for internal combustion engines generally include a center electrode and a ground electrode. Traditionally, the center electrode may be of a cylindrical shape and the ground electrode may be of a columnar shape having a substantially rectangular cross section. The center electrode and ground electrode define a spark or discharge gap through which a spark extends when the spark plug is firing as intended. Additionally, a noble metal tip may be commonly located at an end of one or both of the electrodes facing the spark gap. Traditional spark plug construction commonly includes attaching these noble metal tips directly to the surface of the electrode, usually on a flat surface near the end or tip of the electrode.
When a noble metal tip is welded to a flat surface with a laser beam, the laser beam melts the base material of the electrode body, but not that of the noble metal tip, thereby creating a connection resembling a braze. Traditionally, the laser welding process securers the noble metal tip to the center electrode and can also be utilized in such a fashion to minimize or avoid cracks or disruptions in the weld between the noble metal tip and the center electrode. By focusing the laser beam on the center electrode body rather than the noble metal tip, the generally cylindrical shape of the center electrode makes it possible for the melted material of the ground electrode body to flow around the noble metal tip in a sufficient manner to form a secure connection without cracks. The shape of the ground electrode, however, does not facilitate a similar free flow of the melted electrode body material, and therefore the resultant braze created between the noble metal tip and the ground electrode is more prone to cracking and less stable than the braze of the center electrode and its noble metal tip.
Accordingly, while existing spark plug electrode welding techniques are suitable for their intended purposes, the need for improvement remains, particularly in providing a ground electrode that allows for the free flow of melted material to form a robust connection with minimal cracking.